The present invention relates to a seat belt retractor for a webbing that permits the webbing to be retracted and withdrawn. More particularly, the present invention relates to a seat belt retractor with a torsion bar for absorbing load exerted on a webbing when an occupant puts on the webbing and the webbing is stopped from being withdrawn in the event of emergency such as a vehicle collision at which large deceleration is exerted on the vehicle.
Conventionally, a seat belt device installed in a vehicle such as an automobile prevents an occupant from being thrown out of a vehicle seat by restraining the occupant with a webbing. The seat belt protects the occupant in the event of emergency such as mentioned above.
A typical seat belt device is provided with a seat belt retractor for accommodating a webbing. When not used, the webbing is fully wound on a reel of the retractor. When an occupant puts on the webbing, the seat belt is withdrawn to extend across the occupant. The seat belt retractor includes a locking mechanism that is activated in the event of emergency as mentioned above to stop the rotation of the reel in an unwinding direction, thereby preventing the webbing from being withdrawn. Therefore, the seat belt webbing can securely restrain and protect the occupant.
However, conventional seat belt retractors being used in seat belt devices have a drawback or problem. That is, when the webbing restrains and protects the occupant, a large deceleration is exerted on the vehicle so that the occupant tends to move forward due to a large inertia force. Accordingly, a large load is exerted on the webbing and the occupant receives a large impact load from the webbing. Thus, there remains a need to absorb the impact load to reduce the discomfort for the occupant. Though this impact load is not so severe for the occupant, it is better to absorb the impact load.
FIG. 8 is a vertical sectional view showing an example of a conventional seat belt retractor 1 including a torsion bar. As shown in the drawing, the seat belt retractor, includes a U-like frame 2, a webbing 3, a reel 4 which is rotatably supported between side walls of the U-like frame 2 and on which the webbing 3 is wound, a deceleration sensing means 5 which detects a large deceleration of the vehicle occurred in case of emergency mentioned above, a locking mechanism 6 which is activated by the deceleration sensing means 5 to prevent the reel from rotating in the webbing unwinding direction, a torsion bar 7 loosely fitted and inserted in the axial direction in the center of the reel 4 and which rotatably connects the reel 4 and the locking mechanism 6, a spring means 8 for always biasing the reel 4 in the webbing winding direction through a bush 10 by the spring force of a spiral spring 9, a pretensioner 11 which is activated in the case of emergency mentioned above for producing webbing winding torque, and a bush 12 for transmitting the webbing winding torque of the pretensioner 11 to the reel 4.
The locking mechanism 6 include a pawl holder 14 which rotates together with a first torque transmitting portion 17 of the torsion bar 7. The holder 14 pivotally holds the pawl 13 and also includes a lock gear 6a which rotates together with the torsion bar 7 during normal operation. The lock gear 6a stops in an emergency corresponding to the activation of the deceleration sensing means 5 to produce rotation relative to the torsion bar 7 and engages the pawl 13 with one of internal teeth 19 of the side wall of the frame 2, thereby stopping the rotation of the pawl holder 14 and the rotation of the reel 4 in the webbing unwinding direction. The pawl holder 14 has an external thread portion 15 that includes a nut-like stopper member 16 which rotates together with the reel 4 and is screwed into the thread portion 15.
The torsion bar 7 includes the first torque transmitting portion 17 which is fitted to the pawl holder 14 not allowing relative rotation therebetween, and a second torque transmitting portion 18 which is fitted to the reel 4 not allowing relative rotation therebetween.
The reel 4 is always biased by the spring force of the spring means 8 in the webbing winding direction through the bush 10, the torsion bar 7, the second torque transmitting portion 18 of the torsion bar 7, and the bush 12. The webbing winding torque produced by the pretensioner 11 is transmitted to the reel 4 through the bush 12 whereby the reel 4 winds up the webbing 3 a predetermined amount.
In the conventional seat belt retractor 1 having the aforementioned structure, the webbing 3 is fully wound up by the biasing force of the spring means 8 when not being used by a vehicle passenger. As the webbing 3 is withdrawn at a normal speed for putting on, the reel 4 rotates in the webbing unwinding direction so that the webbing 3 is smoothly withdrawn. After a tongue (not shown) slidably fitted to the webbing 3 is inserted into and engaged with a buckle fixed to a vehicle body, the excess amount of the webbing 3 is wound back onto the reel 4 by the biasing force of the spring means 8 until the webbing 3 is fitted to the occupant""s body without excess stress.
In an emergency, such as mentioned above, the webbing winding torque produced by the pretensioner 11 is transmitted to the reel 4 so that the reel 4 winds up the webbing 3 for a predetermined amount, in order to strongly restrain the occupant. The deceleration sensing means 5 is activated by a large deceleration produced by the emergency condition to activate the locking mechanism 6. The activation of the deceleration sensing means 5 prevents the rotation of the lock gear 6a in the webbing unwinding direction. In addition, the pawl 13 of the locking mechanism 6 pivots and engages one of the internal teeth 19 of the side wall of the frame 2 so as to stop the rotation of the pawl holder 14. As a result of this, the reel 4 rotates in the webbing unwinding direction relative to the pawl holder 14 while the torsion bar 7 is twisted. By this twisting of the torsion bar 7, the load applied to the webbing 3 is limited, thus absorbing the impact on the occupant.
Since the reel 4 rotates relative to the paw holder 14, the stopper member 16 rotates relative to the external thread portion 15 which is screwed into the stopper member 16, whereby the stopper member 16 moves toward the pawl holder 14. When stopper member 16 comes into contact with the pawl holder 14, the stopper member 16 is prevented from further rotation. As a result, the reel 4 is also prevented from rotating and the torsion bar 7 is prevented from being twisted. In this manner, the webbing 3 is stopped from being withdrawn whereby the occupant is restrained by the webbing 3. Thus, the movement of the stopper member 16 defines the maximum allowable twisting deformation of the torsion bar 7. Through adjustment the EA (xe2x80x9cEnergy Absorbingxe2x80x9d) stroke as a rotatable stroke of the reel 4 relative to the pawl holder 14 can be freely set.
In addition, in the conventional seat belt retractor 1, the pawl holder 14 of the locking mechanism 6 rotates in the webbing unwinding direction relative to the lock gear 6a when the webbing is rapidly withdrawn. Also in this case, the pawl 13 of the locking mechanism 6 engages one of the internal teeth 19 of the side wall of the frame 2 so as to stop the rotation of the pawl holder 14 in the same manner as mentioned above. Therefore, the reel 4 is prevented from rotating in the unwinding direction through the torsion bar 7, thus stopping the withdrawal of the webbing.
In the conventional seat belt retractor 1, the torsion bar 7 extends to penetrate the bush 12. The bush 12 is sandwiched between the second torque transmitting portion 18 of the torsion bar 7 and an E-ring 20 fitted to a groove of the torsion bar 7 whereby the movement of the torsion bar 7 in the axial direction relative to the bush 12 is limited. The relative movement of the bush 12 in the axial direction relative to the frame 2 is limited. Thus, the movement of the torsion bar 7 relative to the frame 2 is limited. The torsion bar 7 is fixed in the axial direction relative to the frame 2 and the reel 4.
In the conventional seat belt retractor 1, the groove in which the E-ring 20 is fitted is required to be formed in the torsion bar 7. This arrangement complicates the configuration of the torsion bar 7. In addition, since the torsion bar 7 extends to penetrate the bush 12, the torsion bar 7 should have a long axial length.
Furthermore, there can be backlash due to the dimensional tolerance between the E-ring 20 and the groove in which the E-ring 20 is fitted. The backlash may cause a jarring noise when the vehicle vibrates for running. A mechanism must be provided to reduce the jarring noise. Thus, the structure for fixing the torsion bar 7 in the axial direction is complex thereby reducing the workability of assembling the torsion bar 7, and increasing the cost.
Thus, there remains a need for a seat belt retractor which can be manufactured at a low cost and which can realize the simplification of the configuration of a torsion bar, the simplification of the structure for fixing the torsion bar in the axial direction, and the improvement of the workability of assembling the torsion bar, and can prevent the occurrence of a jarring noise.
To solve the aforementioned problems, an improved seat belt retractor is provided. The seat belt retractor comprises a reel for winding up a webbing; a locking means for preventing the rotation of the reel in the webbing unwinding direction when actuated; a deceleration sensing means which detects a predetermined deceleration to actuate the locking means; and a torsion bar rotationally connecting the reel and the locking mechanism. The torsion bar having a portion disposed within the reel coaxially with the reel, the torsion bar absorbing load exerted on the webbing when the locking means is actuated. The torsion bar comprises a flange-like first torque transmitting portion which is fitted to the locking means so that the first torque transmitting portion is connected to the locking means to rotate together. The torsion bar also includes a second torque transmitting portion which is fitted to the reel so that the second torque transmitting portion is connected to the reel to rotate together. The torsion bar further includes a torsion portion which is fixed between the first and second torque transmitting portions and is designed to be twisted to absorb the load exerted on the webbing. One end in the axial direction of at least one of the first and second torque transmitting portions is axially in contact with the corresponding one of the locking means. The reel and the other end of the at least one of the torque transmitting portions is axially in contact with a holder member fitted in the corresponding one of the locking means and the reel.
According to an alternative embodiment of the present invention, a seat belt retractor is provided. The seat belt retractor comprises a reel for winding up a webbing; a locking means for preventing the rotation of the reel in the webbing unwinding direction when actuated; a deceleration sensing means which detects a predetermined deceleration to actuate the locking means; and a torsion bar rotationally connecting the reel and the locking mechanism. The torsion bar having a portion disposed within the reel coaxially with the reel. The torsion bar absorbing load exerted on the webbing when the locking means is actuated. The torsion bar comprises a flange-like first torque transmitting portion which is fitted to the locking means so that the first torque transmitting portion is connected to the locking means to rotate together. The torsion bar also includes a second torque transmitting portion which is fitted to the reel so that the second torque transmitting portion is connected to the reel to rotate together. The torsion bar further includes a torsion portion which is fixed between the first and second torque transmitting portions and is designed to be twisted to absorb the load exerted on the webbing. One end in the axial direction of at least one of the first and second torque transmitting portions is axially in contact with the corresponding one of the locking means. The reel and the other end of the at least one of the torque transmitting portions is axially in contact with a crimped portion of the corresponding one of the locking means and the reel.
According to another alternative embodiment of the present invention, a seat belt retractor is provided. The seat belt retractor comprises a reel for winding up a webbing; a locking means for preventing the rotation of the reel in the webbing unwinding direction when actuated; a deceleration sensing means which detects a predetermined deceleration to actuate the locking means; and a torsion bar rotationally connecting the reel and the locking mechanism. The torsion bar having a portion disposed within the reel coaxially with the reel. The torsion bar absorbing load exerted on the webbing when the locking means is actuated. The torsion bar comprises a flange-like first torque transmitting portion which is fitted to the locking means so that the first torque transmitting portion is connected to the locking means to rotate together. The torsion bar also includes a second torque transmitting portion which is fitted to the reel so that the second torque transmitting portion is connected to the reel to rotate together. The torsion bar further includes a torsion portion which is fixed between the first and second torque transmitting portions and is designed to be twisted to absorb the load exerted on the webbing. One end in the axial direction of one of the first and second torque transmitting portions is axially in contact with the corresponding one of the locking means. The reel and the other end of the one of the torque transmitting portions is axially in contact with a holder member fitted in the corresponding one of the locking means and the reel. One end in the axial direction of the other one of the first and second torque transmitting portions is in axially in contact with the other corresponding one of the locking means. The reel and the other end of the other one of the torque transmitting portions is axially in contact with a crimped portion of the other corresponding one of the locking means and the reel.
Furthermore, the holder member may be composed of a pin having a slope(s) where it comes in contact with the torque transmitting portion.
Furthermore, the holder member may further includes a slit(s) formed in the portion where comes in contact with the torque transmitting portion so as to elastically press the torque transmitting portion in the axial direction.
Furthermore, the holder member may be composed of a plate to elastically press the torque transmitting portion in the axial direction.
In addition, the holder member may be composed of a pin having a first engaging protrusion at one end thereof and a first engaging protrusion at the other end thereof. A member into which the holder member is fitted is formed with a holder-member-fitting hole having two stepped portions. The first engaging protrusion is engaged with one of the stepped portions and the second engaging protrusion is engaged with the other one of the stepped portions when the holder member is inserted into the holder-member-fitting hole. As a result, the torque transmitting portion is brought in contact with a middle portion of the pin.
Moreover, at least one of the first and second torque transmitting portions may be formed in serration, to have a TORX-wrench-like section, or to have a hexagonal section.
At least one of the first and second torque transmitting portions may be clamped between one of the locking means and the reel, into which the at least one of torque transmitting portions is fitted, and the holder member in the axial direction. Alternatively, at least one of the first and second torque transmitting portions is fixed by crimping one of the locking means and the reel into which the at least one of torque transmitting portions is fitted. Alternatively, one of the first and second torque transmitting portions may be clamped between one of the locking means and the reel, into which the at least one of torque transmitting portions is fitted, and the holder member in the axial direction. The other one of the first and second torque transmitting portions may be fixed by crimping one of the locking means and the reel into which the at least one of torque transmitting portions is fitted.
Accordingly, at least one of the first and second torque transmitting portions conventionally formed in the torsion bar is effectively used. Therefore, a groove into which an E-ring conventionally used for the torsion bar can be eliminated, thereby simplifying the configuration of the torsion bar and simplifying the working for the torsion bar.
At least one of the first and second torque transmitting portions may be strictly fixed without backlash in the axial direction. Therefore, the occurrence of jarring noise due to vibrations or the like of the seat belt retractor can be prevented. The torque transmission can be further secured.
As apparent from the above description, at least one of first and second torque transmitting portions conventionally formed in a torsion bar is effectively used to fix the torsion bar in the axial direction. An E-ring as conventionally used for the torsion bar can be eliminated, thereby simplifying the configuration of the torsion bar. Therefore, the working for assembling the torsion bar is also simplified and the manufacturing cost of the torsion bar can be reduced.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.